1. Field of the Invention
This invention relates generally to safety devices for use in the construction industry and more particularly to a sheeting installation system and frame which are utilized to install trench wall support sheeting sections in overlappping relationship during trench excavations and the like to prevent the sides of the trench from collapsing.
2. Description of the Prior Art
A serious safety problem exists during the underground installation of sewer and water pipes and the like where substantially narrow, but deep, trenches must be excavated. If a back hoe or similar piece of mechanical excavation equipment is utilized, the sides or walls of the trench are substantially vertical and are sharply defined, thereby increasing the possibility that the sides of the trench may collapse to cause death or injury to workmen working at the bottom of the trench. Although so-called "safety drag boxes" have been developed which are lowered into the trench after excavation to prevent the walls of the trench from collapsing, the condition of the soil in the area being excavated very often precludes the use of such devices. For example, in areas where the ground is very wet or has a very high sand content, the removal of the drag box by lifting it out of the trench or dragging it along the trench to the next working location could cause the trench walls to collapse or the ground at the bottom of the trench to shift and thereby disturb the pipe being installed from its prescribed location. In situations of this type, it is customary for the engineering specifications for the job to provide for the use of trench wall support sheeting by the contractor. The support sheeting usually consists of sections of steel sheets or sections formed of wood planking which are driven into the ground along the proposed side lines of the trench. Although wood sheeting sections are still used in some areas, it has become customary to use steel plate sheeting sections because of the greater strength and safety offered. The sheeting sections may be completely flat or may be corrugated to increase their lateral or bending strength.
At the present time, the installation of trench wall sheeting is a laborious, time-consuming and expensive operation. The first step usually involves the fabrication of a rectangular, steel support assembly which has a width corresponding to the width of the proposed trench. The four members of the assembly are usually cut to the required length and assembled at the job site from narrow widths of steel channels, beams or angles. When the first assembly is completed, it is placed on the ground in alignment with the proposed side walls of the trench and the steel sheeting sections are placed along the outside edge or periphery of the frame along the trench lines. The sheeting sections are then driven down into the earth for a specified distance and the earth between the sheeting is then excavated. At this time, a second steel support assembly is fabricated and is lowered into the trench where it is wedged into position between the sheeting sections on opposite sides of the trench to resist the lateral forces exerted by the sidewalls of the trench. The sheeting is then driven down a further distance and another rectangular support assembly is installed. This process is repeated until the bottom of the trench is reached. The number of support assemblies utilized and the number of steps involved will, of course, depend upon the depth of the trench. After the pipe or utility main is laid on the floor of the trench, the sheeting is withdrawn in increments or steps and the support assemblies are successively removed as the earth is filled back into the trench.
Although support assemblies of the foregoing type have been developed where the assembly members are hinged together at the corners to permit the assemblies to be collapsed and transported from a completed section of the trench to the next section to be excavated, the time and labor costs involved in fabricating the assemblies, installing the various assemblies at the different depths in the trench, removing the individual assemblies and transporting them to the next section of trench are very substantial and greatly add to the overall cost of the job. Sheeting installation systems have also been developed which utilize sheeting support frames in which relatively thick wood or metal planks having a small surface area are supported by vertically-disposed guide members or channels in the frame while they are being driven into the earth. These systems are not suited for the installation of the newer types of sheeting in which the sheeting sections comprise relatively thin sheets, either corrugated or uncorrugated, having a large surface area because the guide members or channels provide insufficient lateral support to prevent bending of the sheets about a vertical axis which is perpendicular to the plane of the earth's surface. Corrugated sheeting having vertically-disposed corrugations has sufficient structural strength to prevent bending about a horizontal axis which is parallel to the plane of the earth's surface but has a much lower strength with respect to bending about the aforementioned vertical axis. Because of the tendency of the newer types of sheeting to bend about the vertical axis, it is important that the sheeting sections be overlapped when they are installed so that any vertical axis bending caused by the laterally-applied force of the trench walls will not separate the sheeting sections and permit earth and sand to enter the trench. Apart from the sheeting section bending problem, the use of overlapped sheeting sections is important when work is done in areas having a high sand content or very wet earth since even a small separation between adjacent sheeting sections will permit a large volume of sand or earth to enter the excavated trench. The construction of the guide members of known types of sheeting installation frames actually prevents the sheeting sections from being overlapped as they are installed. Furthermore, the existing types of installation frames do not provide for enclosure of the guide members to prevent injury to workmen in the trench as the sheeting sections are being driven into position.
Accordingly, a need exists for equipment which will facilitate the installation of support sheeting by eliminating job site fabrication of support assemblies and the time-consuming steps of installing and removing the separate support assemblies for each length of trench being excavated. Additionally, a substantial need exists for a sheeting installation frame which will permit the installation of the newer types of sheeting in overlapped relationship and which offers a closed guide slot construction for worker safety. The sheeting installation frame should also be mechanically rugged and be easily transported from one section of the trench to the next. The equipment should also be adjustable to handle trenches of different widths and should be able to accomodate standard or special sheeting sections. Finally, means should be provided to permit the sheeting sections to be moved with the installation equipment when the equipment is moved along the trench.